In recent years, a commodity management by POS system (point of sales system) has been executed very actively. The optical device for reading information like a bar code reader has been used for the POS system.
Namely, such data processing as an inventory management has been executed by displaying the information about the commodities (a kind of commodities and cost of commodities and so on)in a bar code as an information medium, reading the bar code with the bar code reader, and processing the information in a host computer.
Recently, also in a physical distribution field, such work as an assortment is often executed by displaying a bar code as an information medium on the commodity and the box, and reading the bar code with a bar code reader.
Some of the devices for reading information like the bar code reader are provided with a device for scanning light. Generally, a method in which the light scanning is executed by revolving a polygon mirror and a galvano mirror mechanically has been adopted for the traditional device for scanning light.
Accordingly, the device for scanning light provided with mechanically movable parts has caused some problems that a controllability is deteriorated and a response delay occurs and so on, and has caused some deficiencies that the optical axis is slipped off by the mechanical vibration and so on.
On the other hand, various methods have been suggested for a display device which displays a stereoscopic picture up to the present. One example is a binocular method represented by a spectacle method in which a cubic effect is obtained by binocular convergence and binocular parallax, letting the left and right eyes look at the different pictures. Besides, a lenticular method of multiple-lens method exists as an extension of the binocular method. A principle of the stereoscopic vision in the lenticular method is the same as the binocular method.
Only unnatural stereoscopic pictures can be seen in such method for stereoscopic display, since no difference (kinetic parallax) occurs in the stereoscopic pictures even if the observer moves his head from left to right.
Holographic stereogram is cited as a method to solve these problems. In holographic stereogram, the natural cubic effect can be obtained even if the observer moves his head from left to right, since the two-dimensional pictures including the parallax are registered in a segment hologram of vertically slender slit form, and a large number of these pictures are arranged horizontally. Besides, holographic stereogram including vertical parallax also exists.
First of all, an object will be photographed moving the camera position vertically if the holographic stereogram which has a vertical parallax is given as an example.
Then, a laser light is applied to the film to which the object was photographed, an object light is beamed by projecting the film against the diffusion board with lens, a slit of a slit board is arranged in front of the hologram dry plate corresponding to the projection position, and the interference fringes are exposure-registered by interfering with the reference light.
Further, a method for preparing an imaged hologram also exists. Namely, the imaged holographic diagram (image type holographic stereogram) is prepared by applying the laser light to the hologram which was prepared as mentioned above so that the light will be converged into the replay light source indicated as a virtual image, installing another hologram dry board in a display position of the image according to the object light wave-front converted by the hologram and exposing the dry board in irradiation of the reference light.
The image type holographic stereogram is capable of displaying the stereoscopic image by applying the replay light to it, reviewing it from the visual region in the wave-front conversion.
It is desirable that the stereoscopic image exists near the holograph surface so as to reduce the fatigue of the observer's eyes, when the stereoscopic display is executed. In the above-mentioned holographic stereogram, it is necessary to image the picture photographed by camera, since the stereoscopic images are replayed so that they will be piled up on the hologram surface.
On the other hand, in the image type holographic stereogram, the hologram surface and the stereoscopic image can be piled up without converting the pictures, since the two-dimensional pictures are on the hologram. Besides, there are some advantages that the image surface will be on the hologram surface and the chromatic aberration will not occur, even if the wavelength of the light which refers to the holograph changes and so on. Accordingly, it can be said that the stereoscopic display by the image type holographic stereogram is easier to see.
Besides, an Audio Optical Deflecting system (AOD) consisting of tellurium dioxide crystal is used as another device for stereoscopic display, and a display device provided with a galvano mirror scanner, polygon mirror and a lens is also known. In the device, the interference fringes formed on the hologram dry board are calculated by the computer from the three-dimensional data of the object which is displayed as a hologram. The data of the interference fringes are written into a frame buffer of the computer, and a picture signal and a synchronization signal are transmitted to the display unit.
In the display unit, the picture signal and the synchronization signal are separated into an optical scanning partial synchronization signal and a hologram signal which activates the audio optical deflecting system from the compound hologram signal for CRT display of the computer. At this moment, the hologram signal should be intermingled with the 100 MHz carrier wave, since the frequency band necessary for activating the audio optical deflecting system is from 50 MHz to 100 MHz. The refractive index variation which is modulated resiliently occurs, when its transmission signal is converted into an ultrasonic wave by the ultrasonic transducer of the audio optical deflecting system (AOD) and the crystal within the audio optical deflecting system (AOD)is transmitted by the ultrasonic wave. The diffracted light can be obtained if the laser light is injected into there. Although a hologram is formed within the audio optical deflecting system (AOD) by these actions, the hologram should be stopped by synchronizing the polygon mirror in sound speed and revolving it, since the hologram is moving in sound speed (slow shear wave of the tellurium dioxide crystal, 617 per second). At this moment, the polygon mirror is also used for scanning the small element holograms horizontally at the same time. The horizontal line hologram formed like this should be scanned vertically by the galvano mirror scanner to replay the three-dimensional image. Accordingly, the three-dimensional image can be seen floating in the space in front of outgoing radiation lens installed behind the polygon mirror.
By the way, the high control accuracy can not be desired and the mechanical control delay can not be avoided, if the device for stereoscopic display owns such mechanically movable parts as the polygon mirror and the galvano mirror scanner. Besides, such problems as the slippage of the light axle due to the occurrence of noises by the mechanical resonance might result in obtaining a stereoscopic picture of poor quality. Further, such maintenance as a mechanical adjustment can not be easily executed.
For this reason, the electronic display of the hologram using, for instance, the spatial light modulation element in which the liquid crystal is used as a deflecting part was also considered. However, although the picture element pitch of the liquid crystal display must be around 1 .mu.m so as to obtain an enough deflection angle (around 30 degrees) when the liquid crystal is used as the deflecting part, it was impossible to do so in reality. Besides, in traditional LCD (Liquid Crystal Display), the spatial frequency of only the integral number twofold of the picture element can be represented, but the deflection of the non-stage using the LCD was inexecutable.
By the way, generally, it is necessary to obtain a phase distribution of the light by the calculation of the computer from the three-dimensional object to be displayed, and it is necessary to calculate the phase distribution from the two-dimensional picture in connection with the image type holographic stereogram, in order to display the hologram electronically by using the spatial light modulation element in which the liquid crystal is used.
The calculation of the phase distribution divides the hologram surface into the microscopic hologram regions, calculates the phase distribution per inaccurate region from the position coordinates and the intensity of all sample points of the object and executes the calculation in connection with all of the microscopic hologram regions. For this reason, the calculation volume is increased considerably also in the image type holographic stereogram in which the phase calculation is executed for the two-dimensional pictures.
Besides, it is necessary to calculate a phase distribution and the load of the computer calculation becomes heavy, whenever the contents of the two-dimensional pictures to be displayed are changed, so the improvement of these points has been desired.
Accordingly, it is desirable that the stereoscopic display can be executed for the image type holographic stereogram without calculating the phase distribution even if the two-dimensional pictures are changed.